For the record, Telegram is barely private (E2EE possible only on secret chats on mobile phone) and entirely un-encrypted for public channels/groups and regular chats.
Telegram as a company has access to all messages and other data that is not in secret chats. They don't cooperate with authorities (at least publicly, but there are allegations about them and Russia). That's one of the reasons why the CEO is in prison.
Signal, on the other hand, cooperates with the government, but since they offer E2EE by default, the information they provide to the government is useless (registration date and/or phone number), because they just don't have any data to provide to begin with.
Correct me if I'm wrong anyone, but I read out the above information doing research these past few days since Durov's arrest.